Balloon catheters are commonly used in endoscopic procedures in the biliary tree, such as to extract stones and calculi obstructing the bile duct or pancreatic duct. In such a procedure, the endoscopist typically performs a sphincterotomy at the opening to the common bile duct then replaces the sphincterotome with a balloon catheter and advances it over the indwelling wire guide past the stone. Contrast media is usually injected prior to introduction of the balloon catheter so that the obstruction can be located fluoroscopically and also, to help determine what size of extraction balloon would be most appropriate. The balloon, which is made of latex or some other compliant material, is then fully inflated in the duct to assess the optimum balloon diameter for sweeping the stone from the duct. Generally there is a predetermined amount of infuscate delivered to achieve the nominal volume and diameter of the balloon. Often the endoscopist will elect to deflate the balloon slightly in order to perform the procedure, especially if the nominal or fully inflated diameter of the balloon is too large for the duct. Another reason is that a fully inflated balloon is more taut and thus, more subject to rupture when contacting a sharp edge of a stone within the duct. A partially deflated balloon is more forgiving and less likely to puncture. One problem with partially deflating the balloon to sweep the stone is that the operator cannot readily determine the diameter of the balloon following deflation and thus, must make an educated guess as to whether it is appropriate for that particular patient's anatomy. The problem is that the calibrations on an inflation device typically refer only to the actual volume being delivered and thus, require that the operator be able to calculate the syringe volume that corresponds to a given balloon size. If a mark is provided that corresponds to the nominal size of that particular balloon, it is of limited use if trying to extrapolate to inflate or deflate to another size. Since the balloon diameter cannot be easily adjusted downward to a known value using a conventional inflation device, a smaller balloon must be used and inflated to the nominal size to achieve certainty of size. This means that the fully inflated smaller balloon may be less forgiving in case of contact with a sharp edge. Because compliant balloons can assume a range of diameters to address a specific need, what is needed is a system that allows the operator to be able to use a single balloon and be able to determine and control the diameter as needed.